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Abstract: Petroleum Resource Assessment of the Wasatch/Mesaverde Petroleum System, Southwestern Uinta Basin


The southwestern Uinta basin's resource assessment is best understood by comparative analysis to the eastern Uinta basin and the operative mechanics and mechanisms of the Wasatch/Mesaverde petroleum system. The eastern system includes the aerial large Greater Natural Buttes Producing Complex. The area is described in the 1995 USGS Resource Assessment as play 2015, with reserve additions estimated to be 2.1 TCF (mean), 1.7 TCF (F50) recoverable.

The southwestern basin is included in the USGS assessment as play 2016, with estimated reserve additions estimated of 0.5 TCF (mean), 0.4 TCF (F50) recoverable. Through 1996, only 13 wells are productive from the Wasatch/Mesaverde system, but several production characteristics demonstrate significantly greater resource potential.

The well-documented relationship between the thermal maturity of basal Mesaverde coals and high EUR wells in the Upper Wasatch from play 2015 continues to the west in the basal Mesaverde Group's Price River and Blackhawk Formation. Stratigraphic analysis of the Wasatch Formation indicate greater thickness of sandstone reservoirs in the western area. Regional seals from the overlying Green River Formation are present, as well as the less well documented laterally-sealing siltstones and shales of the Wasatch Formation and Mesaverde Group.

The complex litho-stratigraphic relationships are transparent to the overwhelming gas expelled from the basal Mesaverde coals. Two major wrench fault systems appear with surface fault-trace patterns indicating classic extensional characteristics that should project to depth. These fault/fracture traces enhance migration pathways as well as fracture permeability in reservoir characterization.

Post-maturation uplift has placed the top of gas shows and production as shallow as 1250 ft (380 m), with maximum drilling depths to the top of the gas displacement envelope of 5000 ft (1525 m).

AAPG Search and Discovery Article #90946©1997 AAPG Rocky Mountain Section Meeting, Denver, Colorado